The invention relates to containers for handling semiconductor wafers, and more particularly to containers for transporting and storing wafer carriers while maintaining a clean environment.
The manufacturing of integrated circuits (ICs) requires an extremely clean environment. ICs are typically manufactured on thin slices of semiconductor materials, such as silicon, called wafers. The fine circuit patterns are fabricated onto the wafer through a sequence of many process steps. These steps are very sensitive to particulate contamination as even very small particles of dust can interfere with the fabrication process and cause defects in the IC. Since particle related defects directly impact the costs of production, increasing the cleanliness of the manufacturing environment has achieved increased productivity by producing higher yields of ICs.
Each process step is performed in sequence by a particular piece of equipment or tool. The wafers are normally transported between tools in carriers (cassettes) that hold many wafers, typically 25, in parallel slots. Thus, upon completion of one process, the cassette of wafers is transported to the next tool for further processing.
The conventional clean room is one method for providing a clean manufacturing environment. Special equipment circulates filtered air throughout the entire room housing all process tools. Personnel working in the room wear special clothing to reduce the particle contamination from themselves. The wafers are processed and transported between tools without leaving the clean room environment. The disadvantages of clean rooms, however, are many. These special rooms are expensive to construct and maintain, and typically encompass very large areas making it difficult to maintain utmost cleanliness. Furthermore, even though specially clothed, the personnel working within the clean rooms are a constant source of particle contamination.
A major improvement over the clean room is the Standard Mechanical Interface (SMIF) system which incorporates the concept of clean mini-environments. Details of a SMIF system are described in the article "SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING", by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115. Each tool or piece of equipment is enclosed within its own small clean environment. Once inside the clean environment of a particular tool, wafers can be manipulated by automated equipment or by personnel using sterile glove ports to reach within. It has been found that such small mini-environments of particle free air having no internal source of particulates provides the cleanest possible environment for manufacturing wafers. Moreover, since the cleanliness of the mini-environment is independent of the external environment, IC manufacturing can proceed in a non-clean facility. The expense and inconvenience of a large clean room is eliminated and process yields of ICs are improved due to the lower concentration of particulate contamination.
A SMIF system comprises three main components:
(1) A small clean environment surrounding the wafer handling mechanism of each process tool. This is typically provided by a canopy over the tool or port through which the cassette of wafers passes into the tool. The canopy isolates the internal environment of the tool from the outside, creating a clean environment for wafer processing. PA1 (2) A small contamination free container or pod (SMIF box) for transporting and or storing a cassette of wafers. The pod maintains a clean environment within. PA1 (3) A mechanical interface whereby the door on the container is designed to mate with the access door of an interface port on the equipment canopy such that the two doors can be opened simultaneously and moved as a unit into the clean interior space, trapping any particles on the external door surfaces between the doors. A particle free interface is thus created whereby the cassette can be transferred between the container and canopy while maintaining a clean environment in both.
In a SMIF system, the container is placed on top of the interface port located on a top area of the tool canopy. Latches release the bottom door on the container and the canopy port access door simultaneously. Because the outside of the container door mates with the outside of the canopy interface port door, most of the particles on the outside of the door are trapped between the two doors. A mechanical elevator lowers the two mated doors, with the cassette riding on top of the doors, into the canopy enclosed mini-environment of the tool. A manual or automated manipulator picks up the cassette and positions it for processing. After processing, the reverse operation takes place, placing the cassette back into the pod for transport to the next tool or for storage.
Semiconductor Equipment and Materials International (SEMI), a consortium of IC manufacturers, has promulgated standards (hereinafter referred to as the Semi-Standards) for the interface port and container door of the SMIF system. The Semi-Standards provide a uniform industry standard so that containers and tool canopy interfaces of different manufacturers can be compatible. One such standard is SEMI E19, 4-92, 200MM "STANDARD MECHANICAL INTERFACE (SMIF)" published in 1992.
While the present SMIF system has proved effective in providing extremely clean environments for fabricating ICs, improvements to the container are needed to increase the system's utility and cleanliness. Present SMIF containers have a lower door designed for a specific interface system such as the Semi-Standard. The interface of each and every clean environment or tool canopy in a particular manufacturing line must be compatible with this one interface so that the wafers can be transported from tool to tool for processing. Installation of an improved or different interface would require the changing of all tool interfaces to maintain compatibility. The prohibitive costs of changing all clean environments simultaneously to a new interface has restricted the development of improved interface systems.
Additionally, the bottom door container has inherent ergonomic problems. Since the cassette is lowered into the clean environment through the bottom door, the container must interface a top area of the clean environment. Personnel transport the containers between tools, constantly lifting the containers to the top of the canopies. Although 6 inch diameter wafers are presently used, the industry is presently switching to heavier 8 inch wafers to increase the number of ICs fabricated on a single wafer. A cassette of 8 inch wafers is much heavier than the 6 inch wafers and much more difficult to handle. One solution proposes an extension or addition of the clean environment canopy having a lower top portion. Once the cassette is lowered within, a robot device raises the cassette to the elevation necessary for the process tool. Such robots, however, are expensive to purchase and maintain. Another solution is an automated device located outside the clean environment canopy which raises the pod from a lower height to the interface port on top of the canopy. This too, however, is expensive to manufacture and maintain.
It is also believed desirable to provide an improved interface seal between the container and the clean environment. Improvements over present interfaces will permit a cleaner manufacturing environment and increased IC yields.
In light of the foregoing, it is a primary object of the present invention to create a container capable of interfacing with more than one particular interface design.
It is a further object of the present invention to provide a container capable of interfacing with the side of a clean environment.
Another object of the present invention is to provide an improved interface system which maintains a cleaner manufacturing environment.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.